Spin torque transfer technology, also referred to as spin electronics, combines semiconductor technology and magnetics, and is a more recent development. In spin electronics, the spin of an electron, rather than the charge, is used to indicate the presence of digital information. The digital information or data, represented as a “0” or “1”, is storable in the alignment of magnetic moments within a magnetic element. The resistance of the magnetic element depends on the moment's alignment or orientation. The stored state is read from the element by detecting the component's resistive state.
The magnetic element, in general, includes a ferromagnetic pinned layer and a ferromagnetic free layer, each having a magnetization orientation that defines the resistance of the overall magnetic element. Such an element is generally referred to as a “spin tunneling junction,” “magnetic tunnel junction”, “magnetic tunnel junction cell”, and the like. When the magnetization orientations of the free layer and pinned layer are parallel, the resistance of the element is low. When the magnetization orientations of the free layer and the pinned layer are antiparallel, the resistance of the element is high.
At least because of their small size, it is desirous to use magnetic tunnel junction elements in many applications. However, their small size also creates issues.
One of the primary issues preventing magnetic tunnel junction elements from replacing other memory elements is the memory cell-to-cell distribution. Significant variations from cell-to-cell exist for magnetic tunnel junction cells. In writing to those cells, the result is a switching field distribution, rather than a constant value; in reading back from those cells, there is variation in resistance and noise. Additionally, thermal stability and stray field sensitivity are issues. Various attempts have been made to provide more stable, more consistent magnetic tunnel junction cells and memory arrays. There is always room for improvement.